The present invention relates to a precoating head for forming a filter cake in a filter carrier, said precoating head comprising an inlet nozzle for the filter aid and a deflection element arranged below the opening of the inlet nozzle for deflecting the flow of filter aid.
WP 93/901 46 discloses a filtering method and a filter device for filtering liquids, wherein the filter cake is first produced in a precoating station within a filter carrier. The carrier is then moved from the precoating station with the filter cake formed therein into a filter in which a plurality of filter carriers are stacked up in tower-like configuration and pressed with one another. Such a filter tower can, e.g., be used for filtering liquids, such as beer or the like.
To achieve a uniform precoating of the filter cake in the precoating station, i.e. a uniform structure of the filter cake with a substantially uniform height, the filter aid, such as kieselguhr, is introduced into a water current via an inlet nozzle on a precoating head of the precoating station and, after having passed through the inlet nozzle, is deflected with the aid of a deflection element in such a manner that it is distributed in the interior of the precoating head above the filter carrier in which the filter cake is to be produced.
It has however been found that a distribution with the aid of a deflection element does not always guarantee the formation of a uniform filter cake, especially on account of resultant swirls which create small craters inside the filter cake that are not desired.
It is therefore the object of the present invention to develop a precoating head of the above-mentioned type in such a manner that a uniform filter cake is formed.
This object is attained with a precoating head of the above-mentioned type in that a distributor grid is arranged in spaced-apart relationship with the deflection element.
It has been found that a distributor grid which is arranged between filter cake and inlet nozzle effects an interruption of the swirls and ensures a very uniform distribution of the liquid containing the filter aid and thus a uniform structure of the filter cake.
The mesh width of the distributor grid depends on the composition of the filter aid, but is between 3 and 12 mm at a wire thickness of from 0.5 to 2 mm when standard kieselguhr preparations are used. The mesh width is always chosen such that the filter aid parts are prevented from settling on the grid.
To accomplish easy cleaning of the distribution grid and to make it replaceable by grids of different mesh widths in response to the respectively intended use, the distribution grid is preferably secured to the side walls of the precoating head in a detachable manner.